Variable pulley transmissions for transferring torque from an input or drive shaft to an output or driven shaft have been used for some time. In these transmissions, a first pulley constructed of a pair of flanges is mounted on the input shaft such that at least one of its flanges is axially movable with respect to its other flange. A second, similarly constructed and adjustable pulley is mounted on the output shaft, and a flexible belt connects the two pulleys to transfer torque therebetween when the input shaft is driven. As the effective diameter of one pulley is changed, the effective diameter of the other pulley is simultaneously changed in the opposite direction to adjust the speed ratio between the input and output shafts in a smooth, continuous manner.
Automotive engineers have long recognized that the maximum operating efficiency of the engine could be achieved if the transmission could be controlled by adjusting to different loads and speed ratios, such that the engine is maintained and operated at its maximum efficiency operating conditions. This is not possible when a conventional geared transmission is teamed with an engine as the speed ratio is adjusted in discrete steps, rather than continuously. Accordingly, efforts have been directed to the use of a continuously variable transmission (CVT) of the type described above, and have resulted in commercial production of passenger cars in which a flexible, continuous rubber belt is used to drivingly connect the pulleys. Rubber belts are subject to wear by reason of the loads they must handle and operation under severe temperature, vibration and other adverse environmental conditions. To improve belt life, flexible belts of metal have been used and considerable effort is being expended to produce inexpensive and durable metal belts. Many of these metal belts are described in the patent literature.
Flexible metal belts for use with CVTs are generally of two varieties, those referred to as "push" belts and those referred to as "pull" belts. An example of a push belt is described in Van Doorne et al U.S. Pat. No. 3,720,113 and an example of a pull belt is described in Cole, Jr. et al U.S. Pat. No. 4,313,730. The belt shown in U.S. Pat. No. 3,720,113 comprises an endless carrier constructed of a plurality of nested metal bands and an endless array of load blocks longitudinally movable along the carrier. Each block has edge surfaces for engaging the pulley flanges of a pulley transmission to transmit torque between the pulleys. The push belt has been used in passenger cars on a limited basis and for some non-automotive, industrial applications. The pull belt of Cole, Jr. et al utilizes an endless chain as the carrier, the sets of links of which are pivotably connected by pivot means, shown as round pins. Generally trapezoidal (when viewed from the front) load blocks encircle the links; however the load blocks in the pull belt of Cole et al are constrained against longitudinal movement along the chain by the pivot means. The patent literature also describes a belt constructed of metal parts joined by pivot means in which the pivot means engage the pulleys of a CVT.
The push belt as described is relatively expensive to manufacture. The pull belt offers a less expensive alternative to the push belt. There are fewer problems in the manufacture of the belt because the links and load blocks (a single member or an assembly of relatively thin plates) can be stamped from sheet metal and the pivot means can be cut from extruded stock.
Aside from costs, a major concern of automotive engineers is noise generation by drive belts for pulley transmissions. Noise of a mixture of frequencies is less objectionable to humans than noise of pure frequencies. Currently an evaluation used by some automotive engineers is to rate noise generated by drive belts of the type described herein in a generally subjective manner by driving or riding in an automobile in which the belt is installed and listening to the generated noise. The noise is then rated on a numerical scale of 1 to 10 with the higher numbers indicating the less objectionable noise. Belts achieving a rating of about 6 and above are usually acceptable for use in automotive drives, and can be classified as being of commercial quality. Of course such belts must also be durable, so as to have a reasonable operating life.
Various ways have been suggested for constructing belts for use in a CVT which operate in such a manner to generate noise acceptable to humans, and a discussion of some of these ways will be found in the prior art. A description of some of the prior art follows.
In the Kern U.S. Pat. No. 4,464,152, a chainbelt constructed in a manner similar to the Cole et al patent, supra, has sound damping means interleaved with load block laminations.
Laster U.S. Pat. No. 4,516,964 discloses load blocks of different transverse widths, all of which contact the pulley flanges, but some at a different radial location on the pulley flanges from others, thus modifying the generated noise pattern.
In Mott U.S. Pat. No. 4,516,965, some load blocks do not contact the pulley flanges, or some load blocks are missing or "skipped", to thus modify the generated noise pattern.
Mott U. S. Pat. No. 4,516,963 discloses a random mixture of load block-pulley flange engaging areas to provide a pattern of random engagement thereof with the pulley flanges, and thus a modified generated noise pattern.
A suggested way to modify the generated noise pattern in a chain in which the pivot means drivingly contact the pulley flanges is to provide a drive chain constructed of a mixture of links of different pitches, such as U.S. Pat. No. 4,344,761, issued Aug. 17, 1982.
Morse U.S. Pat. No. 1,868,334, issued July 19, 1923, teaches constructing a chain for use with sprockets which provides a mixture of distances between adjacent centers of articulation or a mixture of "effective pitches" in order to "break up rythmic vibrations that sometimes cause trouble in chain drives". The patent is silent as to whether or not this "trouble" is noise related.
The invention to be described herein relates to chain and chain-belts which are used to connect sprockets or pulleys of power transmissions. The invention finds particular use for connecting the pulleys of a continuously variable transmission, commonly known as a CVT. In the description which follows, reference will be made to chain, it being understood that this includes not only toothed chains, also known as silent chain, but also structures known as chain-belts which comprise a carrier of connected chain links, pivot means connecting interleaved chain links, and drive blocks each of which encircles a set of links. The invention is primarily applicable to that variety of chain-belt known as pull belts.
In its broadest aspect, the chain is an endless loop and comprises a plurality of links, each defining a pair of longitudinally spaced apertures with one aperture in each link being transversely aligned with an aperture in the next adjacent link to thus form transverse rows of aligned apertures. Pivot means are received in each row of aligned apertures and the pivot means define spaced transverse articulation axes which are parallel to one another. The articulation axes for each link set are longitudinally spaced from each other.
When a chain as thus described is used in a CVT, load blocks encircle the links between each pivot means, the load blocks being generally trapezoidal in shape, when viewed from the front, with the opposing side edges adapted to engage the flanges of the pulleys of the transmission.
Preferably, the pivot means used in the chain comprise a pair of pins, each having the same cross-sectional configuration and differing, if at all, in length. If a clip is used for retaining the pivot means in the assembly of links and blocks, the pins can be substantially the same length. The pins as thus described are similar to that described and claimed in the Cole, Jr. U.S. Pat. No. 4,507,106, and the disclosure therein is incorporated herein by reference. Basically, the pins each have a first, front rocking surface defined by a large radius and a back or link contact surface defined by a plurality of lesser radii.
In chains of the type herein described, the links are arranged as sets. The number of links in a set (and of course the gauge of the metal from which the links are made) determines the ultimate width of the chain. For example, in a narrow chain, it is common to have a 7-8-7 etc. lacing or arrangement with load blocks constructed with a single window encircling each set of links. For a wider chain, a modified load block has been suggested, one with multiple windows such as shown in U.S. Pat. No. 4,512,754, the adjacent windows being separated by a strut. It has been proposed to lace the chain in a 4-5, 5-4, 4-5 etc. pattern, although other lacing arrangements can be used within the purview of the present invention.
The inventive concepts disclosed herein can also be applied to chains usable to connect toothed sprockets, and especially to chains known in the art as "silent" chains in which the links are constructed with at least a pair of projecting toes defined by flanks separated by a crotch. At least some of the flanks contact the sprocket teeth. The problem of noise generation is present in the silent chain-sprocket drive arrangement and is subjectively rated in a manner similar to that described above.